1. Technical Field
The present invention generally relates to extraction of data originating from a physiological phenomenon in a subject, in particular when the vascular system of the subject is in connection with an extracorporeal fluid system. The present invention is e.g. applicable in arrangements for extracorporeal blood treatment.
2. Background Art
Vital signs are measures of various physiological statistics often taken by health professionals in order to assess body functions. Vital signs of a subject, e.g. heart rate, blood pressure, oxygen saturation, electrocardiography (ECG), respiratory rate and autonomous regulation, such as blood pressure and body temperature, may be measured, monitored and interpreted to detect various disorders of the patient, for instance respiratory and heart related disorders. Typical equipment used for retrieving the vital signs includes a thermometer, a pulse oximeter, a capnograph and a pulse watch. Though a pulse may often be taken manually, a stethoscope may be required for a subject with a weak pulse.
With external vital sign monitors, such as a thermometer, a stethoscope, a photoplethysmograph (PPG), a pulse oximeter or a capnograph, it is possible to measure pulse, oxygen saturation and information on respiration, such as breathing rate and carbon-dioxide concentration in breath of patient.
Patients with kidney function insufficiency often suffer from various other disorders, for instance sleep apnea, periodic breathing and hyperventilation, making monitoring of vital signs of renal patients particularly important. Sleep apnea for instance, is a common disorder in the general population where 2%-25% suffer from it, and it correlates with increased rate of several co-morbidities, such as hypertension, coronary artery disease, arrhythmias, heart failure and stroke. The prevalence of apnea is even higher in the dialysis population where 30% to 80% of dialysis patients suffer from this problem. The reason for this is not clear, but it is believed that hypervolemia and high levels of uremic toxins may worsen the disorder. In addition, many dialysis patients (40%) are diagnosed with heart conditions such as angina pectoris, left ventricular hypertrophy, stroke or congestive heart failure. These patients and other subjects may also suffer from reflex-controlled phenomena, such as vomiting, coughing and hiccups. Hence, there is a particular need to monitor vital signs of patients with kidney function insufficiency.
The origin behind the vital signs are for instance physiological pulse generators, such as the breathing system, the autonomous system for blood pressure regulation and the autonomous system for body temperature regulation, which give rise to cyclic physiological phenomena which are known to cause variations in the blood pressure of a patient.
Blood pressure regulation is part of the complex regulatory system which controls arterial blood pressure and is dependent on sensory inputs related to cardiac output, peripheral resistance to blood flow at the arterioles, the viscosity of the blood, the volume of blood in the arterial system, the elasticity of the arterial walls, etc. Changes in blood pressure are brought about by the control exerted on the same physiological mechanisms.
The signals from which information regarding the vital signs are extracted and the sensors being used may vary and instruments for providing this information is often limited in purpose and functionality. Additionally, measurements of vital signs are often time consuming and require involvement and attention from staff competent in handling each instrument.
It is known, for instance from U.S. Pat. No. 5,243,990, of blood pressure monitors, even ones that are included in dialysis machine systems, that allow measurement of the patient's pulse and blood pressure values (e.g. systolic and diastolic pressure) at specified intervals.
To get a good picture of body functions, it is often desirable to monitor a plurality of vital signs, requiring a number of specialised sensors or monitors connected to the body of a patient, which is costly, cumbersome and distracting.
It is also known that coughing and sneezing may influence physiological measurements obtained from instruments. Coughing may for instance introduce errors in the PPG signal e.g. measured with a pulse oximeter.
Hence, there is a need for alternative and/or improved ways of monitoring vital signs for detecting, presenting, tracking and/or predicting disorders, such as disorders related to the respiratory, vascular and autonomous system of the subject.
Furthermore, in extracorporeal blood treatment, blood is taken out of a patient, treated and then reintroduced into the patient by means of an extracorporeal blood flow circuit. Generally, the blood is circulated through the circuit by one or more pumping devices. The circuit is connected to a blood vessel access of the patient, typically via one or more access devices, such as needles or venous catheters, which are inserted into the blood vessel access. Such extracorporeal blood treatments include hemodialysis, hemodiafiltration, hemofiltration, plasmapheresis, etc.
In extracorporeal blood treatment, it is vital to minimize the risk for malfunctions in the extracorporeal blood flow circuit, since these may lead to a potentially life-threatening condition of the patient. Serious conditions may arise if the extracorporeal blood flow circuit is disrupted, e.g. by an access device for blood extraction (e.g. an arterial needle) coming loose from the blood vessel access, causing air to be sucked into the circuit, or by an access device for blood reintroduction (e.g. a venous needle) coming loose from the blood vessel access, causing the patient to be drained of blood within minutes. Other malfunctions may be caused by the blood vessel access becoming blocked or obstructed, or by the access device being positioned too close to the walls of the blood vessel.
In WO 97/10013, the monitoring involves filtering a measured pressure signal to remove the frequency components that originate from a blood pump, and then detecting the heart signal by analysing the filtered pressure signal. The amplitude of the filtered pressure signal is then taken as an indication of the integrity of the fluid connection. This monitoring technique requires proper filtering and might thus fail if there is a significant frequency overlap between the heart signal and the pulses from the blood pump.
Hence, there is also a need for alternative and/or improved ways of monitoring the integrity of a fluid connection between an extra-corporeal circuit and a vascular system of a subject.